<!DOCTYPE html>
<html lang="en">
<head>
    <script src="../js/vue.js"></script>
</head>
<body>
    <div id="app">
        <div>{{a}}</div>
        <div>{{obj.b}}</div>
    </div>
    <script>
        var vm = new Vue({
            el:'#app',
            data : {
                a:'我是根级响应式属性a',
                obj:{}
            }       
        });
        Vue.set(vm.obj,'b','我是Vue.set添加的响应式属性vm.obj');
    </script>
</body>
</html>